Crunch Alert (USA) - hugely serious but (apparently) non-fatal

The tension springs are an essential part of the control circuit to avoid
flutter. Inspection of cables where they go through the adjustment guides
is a standard item on inspection check lists.
It might be smart for everybody to adjust their pedals all the way
forward
and back and see if the guy who did our inspection nissed something.
UH

Not sure that flutter is the reason for the springs. They are necessary to
to tension the cables when the rudder pedals are moved for and aft on some
gliders. Some gliders do not have springs in the cable at all

Originally Posted by Ramy

Renny wrote:[color=blue][i]

Wow, thank god it happened at altitude!
Isn't it that virtually all our rudder pedals mechanism are spring loaded, and if one cable breaks the result is instantaneously full rudder? I always thought this is a receipt for disaster. A glider without rudder control may still be flyable and even landable, but not with full rudder!

Ramy

This is sort of true, but not in this case. The spring is just strong enough to ensure the pedal does not fall forward when the pilot climbs out. Also, if one spring is off, it is not strong enough to allow yaw to initiate.

In the accident of the JS1, the glider was in a right hand slip (full left aileron required). We can assume in this case that the left hand rudder cable broke. In the accident photo’s the right hand cable is off, which probably happened during impact.

On 5/10/2012 6:32 AM, Martin RSA wrote:[color=blue][i]
Ramy;814097 Wrote:
Renny wrote:

Wow, thank god it happened at altitude!
Isn't it that virtually all our rudder pedals mechanism are spring
loaded, and if one cable breaks the result is instantaneously full
rudder? I always thought this is a receipt for disaster. A glider
without rudder control may still be flyable and even landable, but not
with full rudder!

Ramy

This is sort of true, but not in this case. The spring is just strong
enough to ensure the pedal does not fall forward when the pilot climbs
out. Also, if one spring is off, it is not strong enough to allow yaw to
initiate.

In the accident of the JS1, the glider was in a right hand slip (full
left aileron required). We can assume in this case that the left hand
rudder cable broke. In the accident photo’s the right hand cable is off,
which probably happened during impact.


Are the accident photos online?

Originally Posted by Martin Gregorie[_5_]

On Tue, 01 May 2012 20:01:19 +0000, John Firth wrote:

I am surprised that the rudder went full over, and slip would not
center it

I don't think I am, but this would depend on the seating geometry. I've
never seen a JS-1 so have no idea about its seating arrangements.

Here's the general idea. If you fly with knees raised you'll always have
some pressure on the pedals, so if the rudder cable snaps, both pedals
will go forward as described and you'll get full rudder toward the
unbroken cable side.

To let the rudder straighten out it will be necessary to get your feet
off the pedals and keep them off. In some gliders, particularly those
with flat floors, e.g. Discus 1, ASW-19,20 and Pegase, you can probably
pull your knees up and put your feet flat on the floor with your toes
resting against the pedal hinge bar if necessary. In a DG-300 you can
probably pull your knees toward you with your lower legs and heels
resting on the 'shelf' behind the pedals. However, in other gliders where
you fly with raised knees there are problems. If there isn't the space to
put your feet flat on the floor behind the pedal hinges this will be
extremely tiring after the first 5-10 minutes. Would it be possible at
all in an LS7 or 8? I have no idea if there's any foot room between the
front of the under-knee hump and the pedal pivots in these gliders.

WE should test controlability with feet off!

And also see if its possible to take your feet entirely off the pedals
and keep them off for the time it will take to pick a field, lose height,
fly a circuit and land. If this requires holding your legs and/or feet in
the air, can you do that long enough to land the glider without the
effort of doing it being totally distracting?


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Pulling your feet off the pedals will make little difference in most modern gliders as the pedals have springs on them to keep some tension on the cables. A guy in my club had a rudder cable let go in his Discus B some years ago and had the rudder go hard over. He spun, came out in a spiral dive tried to see how slow it was controllable, spun it again recovering too low to bail out so landed out with plenty of speed in a semi controlled fashion. Blew the tire and walked away

In January 2009 a Lak 12 had a rudder cable break while flying at Omarama. The pilot in this case had the rudder go over but was able to maintain a slipping turn down to a landout. Glider was crunched in a fence but pilot walked away.

It would appear the rudder will go over and if you resort to a slipping turn the rudder will stream more to the side the spring is pulling it towards

[quote=Greg Arnold;

Are the accident photos online?[/QUOTE]

Not that I am aware of

snip

It would appear the rudder will go over and if you resort to a slipping turn the rudder will stream more to the side the spring is pulling it towards[/quote]

Further to my earlier post, an excerpt from a Derek Piggot article primarily about the Janus C that makes interesting reading

On May 10, 7:32*am, Martin RSA joburgatgeerlingsdotcodotza wrote:[color=blue][i]
Ramy;814097 Wrote:

Renny wrote:

Wow, thank god it happened at altitude!
Isn't it that virtually all our rudder pedals mechanism are spring
loaded, and if one cable breaks the result is instantaneously full
rudder? I always thought this is a receipt for disaster. A glider
without rudder control may still be flyable and even landable, but not
with full rudder!

Ramy

This is sort of true, but not in this case. The spring is just strong
enough to ensure the pedal does not fall forward when the pilot climbs
out. Also, if one spring is off, it is not strong enough to allow yaw to
initiate.

In the accident of the JS1, the glider was in a right hand slip (full
left aileron required). We can assume in this case that the left hand
rudder cable broke. In the accident photo’s the right hand cable is off,
which probably happened during impact.

--
Martin RSA

Saw the photos yesterday. Also inspected the sister ship of the JS1
that had a rudder cable failure at 100 hours. The sister ship has 28
hours and the right rudder cable is beginning to fray with several
strands already worn through due to contact with the sharp edge of the
S tube.